1. Field of the Invention
The present invention relates to a drive unit for electrically driven remote-controlled mirror, and more particularly to an improved drive mechanism which slants a mirror body pivotably supported inside a mirror housing and to which a mirror is secured, around a horizontal and vertical axes passing through the central axis of a pivot.
2. Description of the Prior Art
In a conventional drive unit for slanting the mirror of an electric remote control mirror apparatus (disclosed for example in U.S. Pat. No. 4,696,555), the mirror body to which the mirror is fixed is pivotably disposed in relation to a seat or receptacle formed on the surface of a drive unit casing disposed within the mirror housing and which includes two drive motors and a group of reduction gears. In such drive unit, a pair of internally threaded cylindrical screw rods is inserted into two openings, respectively, formed on two straight lines passing through the center of the seat formed on the drive unit casing and which are nearly perpendicular to each other, the screw rods being movable in a direction generally perpendicular to the surface of the drive unit casing but blocked against rotation. The end of each screw rod is connected, as blocked against rotation, to the seat formed on the rear side of the mirror body, and rotating shaft members having a pair of arm members provided with a pair of external thread portions in mesh with the internal threads, respectively, of the screw rods are rotatably supported around shafts formed on the bottom wall in the drive unit casing. Further, a hollow cylindrical gear member having on the outer cylindrical circumference thereof a gear in mesh with the last reduction gear among the drive reduction gears in group is disposed so as to rotate with the rotating shaft member, and the screw rods are housed in the hollow portions, respectively, of the gear members.
In such mirror drive unit, the rotation of the motor is converted into a rotation of the gear member and the rotating shaft member through the reduction gear group, and further it is transmitted to the internal thread of the screw rod, in mesh with the external thread of the rotating shaft member. Since each of the screw rods is blocked against rotating, the screw rod itself are axially moved forwardlY or backwardly depending upon the rotating direction of the motor. The substantial forward or backward movement of each screw rod causes the mirror body to slant around the horizontal or vertical axis pivoting around the center pivot. The outer circumference of each screw rod is in contact with the O-ring disposed within the drive unit casing and surrounding an opening formed in the drive unit casing, the internal thread form on the inner circumference of each screw rod is in mesh with the external thread formed on the ends of the arm members in pair formed on the top of the rotating shaft member, and a U-shaped spring is disposed between the arm members in pair and which always presses elastically the pair of external threads of the rotating shaft member to the internal threads of the screw rods. Since follows up with the pivoting movement around the center pivot of the mirror body within a predetermined angle, each of the screw rods is forcibly slanted with respect to the axial center in practice when it is moved forwardly or backwardly, so that the pair of arm members is forcibly deformed according to the slant of each screw rod while the external thread formed on the end of each arm member is kept in mesh with the external thread of each screw rod. The base of each rotating shaft member is rotatably supported around a shaft formed on the bottom wall inside the drive unit casing. The deformation of the arm members in pair causes the friction between the internal threads of the screw rods and the pair of external threads in mesh with the internal threads to increase, with the result that the motor for moving forwardly or backwardly each screw rod is applied with an extra load.